<form action="<?php echo $_SESSION['purchaseURL']; ?>" method="POST" id="SagePayForm" name="SagePayForm">
  <input type="hidden" name="navigate" value="" />
  <input type="hidden" name="VPSProtocol" value="<?php echo $data['protocol'] ?>">
  <input type="hidden" name="TxType" value="<?php echo $data['transactiontype'] ?>">
  <input type="hidden" name="Vendor" value="<?php echo $data['vendor_name'] ?>">
  <input type="hidden" name="Crypt" value="<?php echo $_SESSION['crypt'] ?>">
  <input type="submit" value="Submit" />
</form>